System and method for measuring the linear and rotational acceleration of a body part

ABSTRACT

A system and method for determining the magnitude of linear and rotational acceleration of and direction of impact to a body part, such as a head includes positioning a number of single-axis accelerometers proximate to the outer surface of the body part. A number of accelerometers are oriented to sense respective linear acceleration orthogonal to the outer surface of the body part. The acceleration data sensed is collected and recorded. A hit profile function is determined from the configuration of the body part and the positioning of the plurality of accelerometers thereabout. A number of potential hit results are generated from the hit profile function and then compared to the acceleration data sensed by the accelerometers. One of the potential hit results is best fit matched to the acceleration data to determine a best fit hit result, which yields the magnitude of linear acceleration to and direction of an impact to the body part. The rotational acceleration of the body part can also be estimated from the magnitude of linear acceleration of and direction of the impact to the body part.

[0001] This application claims the benefit of the ProvisionalApplication No. 60/239,379, filed Oct. 11, 2000.

GOVERNMENT RIGHTS

[0002] The invention described herein was made in the course of workunder grant number 1R43HD4074301 from the National Institutes of Health.The U.S. Government may retain certain rights in this invention.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to recording of the magnitude anddirection of impact to and the linear and rotational acceleration of abody part, such as a human head, of person engaged in physical activity,such as during the play of a sport.

[0004] More particularly, it relates to a helmet based system which istypically worn while playing a sport such as football or hockey, and tothe method of recording and storing data relating to the linear androtational accelerations of the person's body part due to impact forcesacting thereon. The present invention relates also to head mountedsystems which are also worn during game play, such as a head band, thatdoes not employ helmets, such as soccer.

[0005] It should be understood that the present invention relatesgenerally to the linear and rotational acceleration of a body part, andmost importantly, the head. The present invention, as will be discussedin detail below, is capable of monitoring any body part of an individualbut has particular application in monitoring the human head. Therefore,any reference to a body part is understood to encompass the head and anyreference to the head alone is intended to include applicability to anybody part. For ease of discussion and illustration, discussion of theprior art and the present invention is directed to the head of human, byway of example and is not intended to limit the scope of discussion tothe human head.

[0006] There is a concern in various contact sports, such as footballand hockey, of brain injury due to impact to the head. During suchphysical activity, the head or other body part of the individual, isoften subjected to direct contact to the head which results in impact tothe skull and brain of the individual as well as movement of the head orbody part itself.

[0007] Much remains unknown about the response of the brain to headaccelerations in the linear and rotational directions and even lessabout the correspondence between specific impact forces and injury,particularly with respect to injuries caused by repeated exposure toimpact forces of a lower level than those that result in a catastrophicinjury or fatality. Almost all of what is known is derived from animalstudies, studies of cadavers under specific directional and predictableforces (i.e. a head-on collision test), from crash a dummies, from humanvolunteers in well-defined but limited impact exposures or from othersimplistic mechanical models. The conventional application of knownforces and/or measurement of forces applied to animals, cadavers, crashdummies, and human volunteers limit our knowledge of a relationshipbetween forces applied to a living human head and resultant severe andcatastrophic brain injury. These prior studies have limited value asthey typically relate to research in the automobile safety area.

[0008] The concern for sports-related injuries, particularly to thehead, is higher than ever. The Center for Disease Control and Preventionestimates that the incidence of sports-related mild traumatic braininjury (MTBI) approaches 300,000 annually in the United States.Approximately ⅓ of these injuries occur in football. MTBI is a majorsource of lost player time. Head injuries accounted for 13.3% of allfootball injuries to boys and 4.4% of all soccer injuries to both boysand girls in a large study of high school sports injuries. Approximately62,800 MTBI cases occur annually among high school varsity athletes,with football accounting for about 63% of cases. Concussions in hockeyaffect 10% of the athletes and make up 12%-14% of all injuries.

[0009] For example, a typical range of 4-6 concussions per year in afootball team of 90 players (7%), and 6 per year from a hockey team with28 players (21%) is not uncommon. In rugby, concussion can affect asmany as 40% of players on a team each year. Concussions, particularlywhen repeated multiple times, significantly threaten the long-termhealth of the athlete. The health care costs associated with MTBI insports are estimated to be in the hundreds of millions annually. TheNational Center for Injury Prevention and Control considerssports-related traumatic brain injury (mild and severe) an importantpublic health problem because of the high incidence of these injuries,the relative youth of those being injured with possible long termdisability, and the danger of cumulative effects from repeat incidences.

[0010] Athletes who suffer head impacts during a practice or gamesituation often find it difficult to assess the severity of the blow.Physicians, trainers, and coaches utilize standard neurologicalexaminations and cognitive questioning to determine the relativeseverity of the impact and its effect on the athlete. Return to playdecisions can be strongly influenced by parents and coaches who want astar player back on the field. Subsequent impacts following an initialconcussion (MTBI) may be 4-6 times more likely to result in a second,often more severe, brain injury. Significant advances in the diagnosis,categorization, and post-injury management of concussions have led tothe development of the Standardized Assessment of Concussion (SAC),which includes guidelines for on-field assessment and return to sportcriteria. Yet there are no objective biomechanical measures directlyrelated to the impact used for diagnostic purposes. Critical clinicaldecisions are often made on the field immediately following the impactevent, including whether an athlete can continue playing. Data from theactual event would provide additional objective data to augmentpsychometric measures currently used by the on-site medicalpractitioner.

[0011] Brain injury following impact occurs at the tissue and cellularlevel, and is both complex and not fully understood. Increased braintissue strain, pressure waves, and pressure gradients within the skullhave been linked with specific brain injury mechanisms. Linear androtational head acceleration are input conditions during an impact. Bothdirect and inertial (i.e. whiplash) loading of the head result in linearand rotational head acceleration. Head acceleration induces strainpatterns in brain tissue, which may cause injury. There is significantcontroversy regarding what biomechanical information is required topredict the likelihood and severity of MTBI. Direct measurement of braindynamics during impact is extremely difficult in humans.

[0012] Head acceleration, on the other hand, can be more readilymeasured; its relationship to severe brain injury has been postulatedand tested for more than 50 years. Both linear and rotationalacceleration of the head play an important role in producing diffuseinjuries to the brain. The relative contributions of these accelerationsto specific injury mechanisms have not been conclusively established.The numerous mechanisms theorized to result in brain injury have beenevaluated in cadaveric and animal models, surrogate models, and computermodels. Prospective clinical studies combining head impact biomechanicsand clinical outcomes have been strongly urged. Validation of thevarious hypotheses and models linking tissue and cellular levelparameters with MTBI in sports requires field data that directlycorrelates specific kinematic inputs with post-impact trauma in humans.

[0013] In the prior art, conventional devices have employed testingapproaches which do not relate to devices which can be worn by livinghuman beings, such as the use of dummies. When studying impact withdummies, they are typically secured to sleds with a known accelerationand impact velocity. The dummy head then impacts with a target, and theaccelerations experienced by the head are recorded. Impact studies usingcadavers are performed for determining the impact forces and pressureswhich cause skull fractures and catastrophic brain injury.

[0014] There is a critical lack of information about what motions andimpact forces lead to MTBI in sports. Previous research on footballhelmet impacts in actual game situations yielded helmet impactmagnitudes as high as 530 g's for a duration of 60 msec and >1000 g'sfor unknown durations with no known MTBI. Accelerometers were heldfirmly to the head via the suspension mechanism in the helmet and withVelcro straps. A recent study found maximum helmet accelerations of 120g's and 150 g's in a football player and hockey player, respectively.The disparity in maximum values among these limited data setsdemonstrates the need for additional large-scale data collection.

[0015] Most prior art attempts relate to testing in a lab environment.However, the playing field is a more appropriate testing environment foraccumulating data regarding impact to the head. A limitation of theprior art involves practical application and widespread use ofmeasurement technologies that are size and cost effective forindividuals and teams. Therefore, there would be significant advantageto outfitting an entire playing team with a recording system tomonitoring impact activities. This would assist in accumulating data ofall impacts to the head, independent of severity level, to study theoverall profile of head impacts for a given sport. Also, full-time headacceleration monitoring would also be of great assistance inunderstanding a particular impact or sequence of impacts to a player'shead over time that may have caused an injury and to better treat thatinjury medically.

[0016] To address this need, there have been many attempts in the priorart to provide a system for recording the acceleration of anindividual's body part, such as their head. For example, prior artsystems have employed tri-axial accelerometers which are affixed as amodule to the back of a football helmet. Such tri-axial accelerometersprovide acceleration sensing in the X, Y and Z directions which areorthogonal to each other. Tri-axial accelerometer systems require thatthe accelerometers be orthogonal to each other Also, such tri-axialaccelerometer systems have been extremely expensive making it costprohibitive for widespread commercial installation on an entire team.

[0017] Prior art systems, have also attempted to precisely locate thevarious combinations of linear and rotational accelerometers, inspecific orthogonal arrays, within a helmet to obtain completethree-dimensional head kinematics. Such arrays require that theaccelerometers be positioned orthogonal to each other. It isimpractical, from a size, cost and complexity standpoint, for commercialapplication of such arrays in helmet or head mounted systems.

[0018] Obviously, accelerometer arrays for measuring linear androtational accelerations cannot be readily mounted inside the humanhead, as is done with instrumented test dummy heads. Other sensingtechnologies, such as gyroscopes, magnetohydrodynamic angular ratesensors and GPS sensors, do not currently fulfill the practical andtechnical specifications for a commercially available system. Also, theuse of multi-axis accelerometer systems placed in a mouthguard areimpractical because wires need to run from the helmet or backpack intothe user's mouth from the power source and to a telemetry unit, whichmight present a hazard to the players and limited compliance among them.

[0019] In view of the foregoing, there is a demand for a headacceleration sensing system that can be manufactured and installed atvery low cost to permit widespread utilization. There is a demand for asystem that can be installed in many, many individuals, such as anentire football team roster of over 60 players, to provide researchopportunities and data that have not yet been available to thescientific community before. Further, there is a demand for a system andmethod for measuring the linear and rotational acceleration of a bodypart that is easy to install and comfortable for the individual to wear.There is also a desire to provide a low-cost system and method that canrecord and accurately estimate linear and rotational acceleration of abody part.

SUMMARY OF THE INVENTION

[0020] The present invention preserves the advantages of prior art bodypart acceleration systems and associated methods. In addition, itprovides new advantages not found in currently available methods andsystems and overcomes many disadvantages of such currently availablemethods and systems.

[0021] The invention is generally directed to the novel and unique headacceleration monitoring technology that is a highly portable system thatdesigned to measure and record acceleration data in linear directionsand to estimate rotational accelerations of an individual's head anddirection and magnitude of impact during normal activity, such as duringgame play. While the present invention is specifically developed for thehead, monitoring of other body parts, or the body in general, isenvisioned and considered within the scope of the present invention.

[0022] The system and method of the present invention offers theopportunity to study head acceleration, human tolerance limits, therange and direction of accelerations in humans in relation tomorphological features (e.g., neck circumference, head volume, necklength), and the relationship between precise measures of headacceleration in linear and rotational directions and acute consequenceto brain physiology and function. Moreover, it provides the ability tomeasure an individual's cumulative exposure to linear and rotationalaccelerations while allowing unaffected performance of everyday sportsand activities.

[0023] The system and method of the present invention is designed as astandard component of otherwise conventional sporting gear, inparticular the helmet or as an independent head mounted system. Thesystem and method of the present invention is designed for determiningthe magnitude of linear acceleration and direction of impact to a bodypart as well as the rotational acceleration of a body part, such as ahead. A number, such as three, single-axis accelerometers are positionedproximal to the outer surface of the body part and about a circumferenceof the body part in a known spaced apart relation from one another. Theaccelerometers are oriented to sense respective linear accelerationorthogonal to the outer circumference of the body part. Dual-axis ortri-axis accelerometers may also be employed to provide an additionaldirection of acceleration sensing which is tangential to the surface ofthe skull of the head. Such tangential acceleration data may beoptionally employed in further analysis.

[0024] The acceleration data sensed is recorded for each accelerometer.A hit profile function is determined from the configuration (i.e.geometry) of the body part and the positioning of the plurality ofaccelerometers thereabout. A number of potential hit results aregenerated from the hit profile function and then compared to theacceleration data sensed by the accelerometers. One of the potential hitresults is best fit matched to the acceleration data to determine a bestfit hit result. The magnitude acceleration and direction of accelerationdue to an impact to the body part are determined from applying the hitprofile function to the best fit hit result. The rotational accelerationof the body part can also be estimated from the magnitude and directionof the impact to the body part.

[0025] The data recorded is either recorded on a memory card or othermass memory means installed locally in the helmet, or is transmitted toa nearby receiver for storage on a computer's hard drive or otherconventional mass storage device using conventional telemetrytechnology. The present invention provides storage of data over a lengthof time such that cumulative exposure effects and thus limits can beestablished for further or future participation in the sport by theindividual wearing the helmet equipped with the present invention. Thedata also allows detection of impacts to the head which precede theoccurrence of a brain injury. For this purpose the system and method ofthe present invention could be modified to record detailed data onlywhen the accelerations exceed a defined threshold. The data may beprocessed immediately as the data is recorded, or at a later time so asto integrate and otherwise determine the linear, rotational and normalcomponents of acceleration of the player's head.

[0026] The present invention is applicable for use with other parts ofthe body. For instance, other applications could include the study ofthe acceleration of body parts in relation to each other (e.g., amongpole vaulters, high jumpers, or gymnasts), or to understand factorsaffecting acceleration in sprinters and swimmers (e.g., starting andturns).

[0027] Because of its portability, small size, and convenient lightweight, the system and associated method of the present invention canalso be used to study the acceleration of the body parts of liveanimals. For example, the acceleration and deceleration of birds inflight could be studied with a modified version of the presentinvention.

[0028] It is therefore an object of the present invention to employaccelerometers arranged in a manner orthogonal to the surface of thebody part instead of arrays of accelerometers orthogonal to each other.

[0029] It is a further object of the invention to provide an inexpensivesystem that can still achieve results which are within the acceptablerange of error for the given scientific question, study or hypothesis.

[0030] Another object of the present invention is to provide a systemand method of calculating and estimating the linear and rotationalacceleration that is easy to install and is comfortable for theindividual to wear without affecting their game play either in a helmetor head band environment.

[0031] It is yet another object of the present invention to provide asystem and method of measuring and calculating the linear and rotationalacceleration that can be installed commercially at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The novel features which are characteristic of the presentinvention are set forth in the appended claims. However, the invention'spreferred embodiments, together with further objects and attendantadvantages, will be best understood by reference to the followingdetailed description taken in connection with the accompanying drawingsin which:

[0033]FIG. 1 is a side view the system of the present inventioninstalled in a football helmet on an individual's head;

[0034]FIG. 2 is a top view of the system shown in FIG. 1;

[0035]FIG. 3 is a schematic top view of a head with a coordinate systemshown thereon;

[0036]FIG. 4 is a perspective view of an accelerometer employed in thepresent invention

[0037]FIG. 5 is a side elevational view of a accelerometer embeddedwithin cushioning of a football helmet;

[0038]FIG. 6 is a side elevational view of an accelerometer held inplace in a helmet by a T-shaped holder;

[0039]FIG. 7 is a diagram illustrating the wireless telemetry systemoptionally employed in the present invention;

[0040]FIG. 8 is a graphical display of the fitting of the algorithm tothe collected data; and

[0041]FIG. 9 is a graphical comparison of simulated peak accelerationand location of impact with ideal peak acceleration and location ofimpact for two sets of accelerometer orientations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] The present invention provides a system and method for measuring,i.e. estimating, the linear and rotational acceleration of a body part.For ease of illustration, the body part will be described below as ahuman head. Unlike the prior art, the present invention uses single axisaccelerometers orthogonal to the surface of the body part and notnecessarily orthogonal to each other to enable the estimation of boththe linear acceleration and rotational acceleration of the body part.

[0043] Referring first to FIG. 1, a side view of an installed system 10of the preferred embodiment of the present invention installed on bodypart 12, namely a human head. FIG. 2 shows a top view of this system 10of the preferred embodiment of the present invention. The system 10includes an array of accelerometers, generally referenced as 14,positioned about the periphery of the skull 16 of the head 12.Preferably, an array of 3 accelerometers 14 or more are located as closeas possible to the outer surface of the skull 16 and arranged in thesame plane which preferably passes through the center of gravity 18 ofthe body part 12. However, less than three accelerometers 14 may be usedand the arrangement of the accelerometers 14 may be in differentconfigurations around the surface of the skull, provided that theirsensitive axis is orthogonal to the surface of the skull. The array ofaccelerometers defines a band about the skull 16 of the head 12.

[0044] In the preferred embodiment shown in FIGS. 1 and 2, an array ofthree accelerometers 14 a, 14 b and 14 c are provided and are positionedat known positions about the outer periphery of the skull 16. As shownin FIG. 2 and in accordance with the coordinate system defined in FIG.3, accelerometer 14 a is positioned at 0 degrees while accelerometer 14b is positioned at 120 degrees and accelerometer 14 c at −120 degrees.The use of as few accelerometers 14 as possible to estimate linear androtational acceleration of the head 12 within a prescribed errortolerance is balanced against the cost associated of the system, namelythe added cost per accelerometer 14 and associated circuitry 15employed. If greater accuracy of the estimation of the linear androtational acceleration of the head 16 is desired, the number ofaccelerometers 14 may be increased to improve the overall “goodness offit” of the actual acceleration measurements to the estimation of linearand rotational acceleration of the head 16.

[0045] The Analog Devices ADXL193/278 family of accelerometers arepreferred for use in the system 10 of the present invention. An exampleof the a preferred accelerometer 14 is shown in FIG. 4. The ADXL278 issimilar to the ADXL 193 except that it is a two-axis accelerometerrather than single-axis. Critical specifications include: small size(4.5 mm×4.5 mm×2.0 mm), low mass (1.5 g), operation at 3.3 V, highoutput (250 g max), high sensitivity (27 mv/g) and low cost. One axismeasures accelerations towards the center of the head, while the secondaxis measures acceleration tangential to the surface of the head. Whilea single-axis accelerometer 14 is preferred, the second axis measurementof the ADXL 278 can also provided additional acceleration informationfor further processing and analysis.. This second axis includesadditional data tangential to the head during rotational experiments inthe laboratory. While the ADXL 193/278 family of accelerometers arepreferred, other accelerometers 14 may be employed to carry out thepresent invention.

[0046] In accordance with the present invention, the accelerometers 14must be held close to the skull 16 of the head 12 to best measure theacceleration of the head. Direct attachment of accelerometers to thehead is optimal but not feasible. Attempts to mount accelerometersdirectly to the helmet shell result in measures of helmet deformationrather than head acceleration. Variations among football helmet paddingand liners and other helmet designs for other sports demand genericmounting concepts that are universally applicable. Thus, the mounting ofthe accelerometers 14 should not alter helmet performance or protrudefrom existing internal padding more than 1 mm. Also, the accelerometers14 should be contained within and/or attached to the helmet to alloweasy removal of both the helmet or headband and the accelerometers 14.

[0047] The present invention provides a structure for maintaining theaccelerometers 14 in a position as close as possible to the skull 16while being as comfortable as possible. As shown in FIG. 5, it has beendiscovered that the preferred structure for positioning of theaccelerometers proximate to the skull is to contain the accelerometers14 within an air bladder 22 mounted within the helmet, generallyreferenced as 20.

[0048] As shown in FIG. 5, the preferred embodiment for carrying theaccelerometers is to capture the accelerometer 14 inside an air-bladder22 itself such that the pressure inside the bladder 22 will provide theforce necessary to place the accelerometer 14 in direct apposition tothe skull 16 of the head 12 when the bladder 22 is inflated. Additionalaccelerometers 14 are respectively placed in appropriately positionedair bladders 22 within the helmet 20 to provided the array ofaccelerometers as described above. In accordance with this attachmentmethod, an RF welding process can be employed to pass the requisitecabling 24 through the bladder seal without compromising the integrityof the bladder 22. A significant advantage of this method is that, for agiven padding configuration, the accelerometers 14 will be orientedsimilarly for all players using that model helmet 20.

[0049] Alternatively, as shown in FIG. 6, the accelerometers 14 may berespectively installed in a plastic T-shaped holder 26 for placing theaccelerometers 14 approximately in apposition to the skull 16 of thehead 12. Each plastic T-shaped holder 26 respectively holds anaccelerometer 14 between the cushions 22 in a football helmet and indirect apposition to the surface of the skull 16. This T-shapedaccelerometer holder 26, for example, may be constructed of Delrin andwith a 4 mm slot 28 for holding and orienting the accelerometer 14. TheT-shaped holder 26 is pressed against the skull 16 of the head 12 whenthe air bladders 22 are inflated to 20 psi, for example. This structurefor positioning the accelerometers 14 may not be preferred because it ispossible that the users could feel the accelerometers 14 pushing againstthe skull 16 of their head 12.

[0050] Also, direct attachment of the accelerometers 14 to the airbladder 22 of the helmet 20 with a foam covering (not shown) ispossible, although not preferred, because the sensitive axis of thesedevices is along a plane parallel to the top of the device. The minimumdimension of the accelerometer 14 and its mounting board 15, as shown inFIG. 4, in that direction is 7 mm, which caused the unit to acteffectively as a point source against the head 12.

[0051] Still further and within the scope of the present invention, amesh net or bandana carrying the array of accelerometers 14 units may beworn on the head or coupled to the inside of the helmet or a multi-layersoft foam interface that captured the accelerometers between layers or aspring-loaded construct attached to the shell of the helmet 20 betweenthe foam pads (not shown) and air bladders 22.

[0052] As shown in FIG. 7, the above described array of accelerometers14 are electrically interconnected together to form an entire system 30for the collection, recording and processing of head acceleration data.The system includes the accelerometers 14 in an array in a head-mountedsensor system (HMSS), generally referred to as 32, an on-board controlunit (OCU), generally referred to as 34, and a base recording station(BRS), generally referred to as 36. Preferably, the data connection 38between the OCU 34 and BRS 36 is preferably wireless, however, ahardwired, tethered connected 38 is also possible. Together, thesecomponents provide a telemetered data acquisition system 30 formonitoring and recording sensor data on head impacts. The installedenvironment for the system 32 need not always be a helmet, and can beadapted for use in various forms in helmets or headgear for sportsincluding football, hockey, soccer, lacrosse, wrestling, boxing andothers. The HMSS unit 32 can be comprised of various additional sensorsincluding displacement, load, pressure, acceleration, temperature, etc.In the current configuration, the HMSS 32 system is composed of multipleaccelerometers 14 as described in detail above.

[0053] In FIG. 7, the BRS 36 and OCU 34 are preferably specified to beactive during all practice and game situations. For team or multipleuser configurations, the BRS 36 is either a laptop or PC 40, which isserially linked to a receiver 42 with capability for simultaneoustransmission from up to 100 OCU transmitters 34. Calculations show thatat a data transfer rate of 19.2 kbps, with maximum 100 bytes ofinformation from each OCU 34 per impact, data from all 22 players on thefield at any one time in sports such as soccer or football could bedownloaded to the BRS 36 within 1 second. For single userconfigurations, the BRS 36 could be a stand-alone data-logger, or couldbe contained internally within the OCU 34, with plug in capability fordownloading of data and programming. Triggering conditions programmedinto the OCU 34 activate the transmitter/data collection system 30 andsend information to the BRS 36. Power is conserved by turning thetransmitter portion of the OCU 34 on only when an impact event occurs.For example, a minimum acceleration of 10 g's might be set as thetrigger. Each OCU 34 uniquely identifies a given helmet 20 in the fieldand encodes the information so that the BRS 36 can properly multiplexand decode information from multiple OCU's.

[0054] In accordance with the present invention, a miniature telemetrysystem 30 is provided with a transmitter/receiver that preferablyoperates in the 900 MHz range with a range of at least 150 m. Analogsignals from the accelerometers 14 will be time-division multiplexed(TDM) for transmission to the BRS. The size of the OCU 34 is specifiedto be no larger than 5 cm long×2.5 cm high×2.5 cm wide, or the size of 2small AA batteries. The OCU 34 can be mounted at the base of the helmet20 in the rear just above the neckline without interfering with playermotion and without creating an injury hazard. The OCU 34 must containthe battery, the transmitter, and signal conditioning for theaccelerometers.

[0055] The preferred accelerometers 14 operate at 3.3 V, the amplifierboards 15 power the accelerometers 14 and provide signal conditioningfor the raw accelerometer signals with a 10 Hz high pass filter toeliminate static measurements (such as player shaking his head). Thechips of the ADXL93/278 accelerometers have a 400 Hz 2-pole Besselfilter on-board. An additional 3000 Hz low pass filter on the amplifierboard reduced high frequency noise that might enter the circuit afterthe accelerometer chip 15 and before the amplifier.

[0056] Details of the above system 30 set forth a preferred constructionfor carrying out the present invention. Such a system 30 may be modifiedto suit the needs of the particular application at hand, namely theenvironment of installation, required capacity, durability and cost.Such modified systems 30 are deemed to be within the scope of thepresent invention.

[0057] Acceleration data is collected and recording for each of theaccelerometers 14 in the system 30 as described above. This data must beprocessed for meaningful analysis. Specifically, in accordance with thepresent invention, the actual linear and rotational acceleration of thehead and the magnitude of the impact is estimated using the arrangementof single-axis accelerometers 14 in the system 30 as described above.

[0058] The data collected and recorded by the accelerometers isprocessed according to a novel algorithm of the present invention. Theprocessing of the data with the novel algorithm of the present inventionassumes that: 1) the accelerometers 14 are placed at known locationsaround the surface of the skull 16 of the head 12, as shown in FIG. 2;and 2) the surface of the skull 16 of the head 12 can be describedgeometrically.

[0059] For example, the novel algorithm can be demonstrated for atypical case where, in addition to the above assumptions, the followingconditions are met: 1) the accelerometers 14 are placed at knownlocations around the transverse plane of the skull 16 of the head 12passing through a point 18 located approximate to the center of gravity,as shown in FIG. 2; 2) the head cross-section (HCS) in this transverseplane is circular, and defines a radial coordinate system, as shown inFIG. 3; and 3) the impact is linear and lies within the transverseplane.

[0060] For these conditions, it can be shown that the magnitude of thelinear acceleration normal to the HCS varies as the cosine of the arc(s) along the HCS. A Hit Profile is defined by the following function:

a*cos(s−b)+c   (1)

[0061] where a=peak linear head acceleration (g's), s=arc (deg), b=hitlocation on the head (deg) and c=the offset. For a given impact and aspecific configuration of accelerometers 14, i.e. the number andlocation of accelerometers 14, there will be a set of n accelerationprofiles and peak accelerations. Given the location of eachaccelerometer, in degrees, in the HCS, a least-squares fit of theacceleration data to the Hit Profile yields the predicted peak linearhead acceleration, a, and the predicted hit location, b, in the HCS. Inthe case where the impact is directed to the center of gravity of thehead 12, the offset will be zero. Otherwise, as will be described below,axial rotational head acceleration will result requiring an offsetvalue.

[0062] In general, the acceleration data is collected and recorded. Ahit profile function is determined from the configuration of the bodypart and the positioning of the plurality of accelerometers thereabout.A number of potential hit results are generated from the hit profilefunction and then compared to the acceleration data sensed by theaccelerometers. One of the potential hit results is best fit matched tothe acceleration data to determine a best fit hit result. The magnitudeand direction of an impact to the body part is determined from applyingthe hit profile function to the best fit hit result. The rotationalacceleration of the body part can also be determined from the magnitudeand direction of the impact to the body part and the offset.

EXAMPLE OF APPLICATION OF ALGORITHM

[0063] As shown in FIG. 8, the acceleration data for a given array ofthree accelerometers is graphically displayed in two dimensions. In thisexample, the accelerometers are placed at the known locations of (−)120degrees, 0 degrees and 120 degrees about the assumed circularcircumference of the skull of a head with a known arc length s which isthe radius r in FIG. 2. In this example, the accelerometers revealed animpact by sensing the following accelerations: TABLE 1 Location ofAccelerometer Peak Acceleration in Coordinate System Sensed (g) (−) 12075    0  8   120 75

[0064] These known parameters of the location of the accelerometers areused to create series of cosine waves from the above algorithm functionwhich are each slightly different than one another. This series ofwaveforms correspond to the various potential hit magnitudes and hitlocations calculated using Equation 1. These waveforms are consideredpotential hit results. As shown in FIG. 8, the series of waveforms 44are mapped over the actual collected data 46. One of the waveforms 44 isselected as a best fit hit result by employing known least squaresregression techniques. The non-selected waveforms are discarded. Theselected best fit hit result, a cosine wave, is governed by thealgorithm function above. Therefore, the additional variables of peaklinear acceleration a and the hit location b in degrees can bedetermined by simply viewing the particular mathematical components ofthe selected best fit result. Thus, the magnitude of the linearacceleration and direction of impact can be calculated using onlysingle-axis accelerometers.

[0065] The function above is employed when the HCS is assumed to becircular. Other functions are employed when the HCS is assumed to beother shapes, such as an ellipse. For an ellipse, the cosine wave hitprofile is modified by multiplication of the tangent of the ellipse andby division of the tangent of a circle. Using a similar approach, thefunction for any geometric shape can be employed to generate the hitprofile for a particular body part shape.

[0066] Further, rotational acceleration is also capable of beingestimated from the linear data obtained from the single-axisaccelerometers 14 and the estimation of the magnitude of accelerationand direction of impact. Specifically, In the case of impacts that arenot directed towards the center of gravity, as shown in FIG. 2, an axialrotational acceleration is assumed to be induced about the z-axis,parallel to the spine through the neck or in the superior-inferiordirection and through the center of gravity 18 of the head 12 The normalcomponent of this rotational acceleration will be recorded by the linearaccelerometers according to the following function:

a_(n)=rω²   (2)

[0067] where r is the distance from the z-axis passing through center ofgravity of the head 12 to the accelerometers 14 and w is the angularvelocity of the head 12. In this case, the algorithm for fitting thelinear acceleration data to the cosine algorithm above worksequivalently and accounts for the offset in linear acceleration data dueto the normal component of angular acceleration. This offset definesaxial rotational acceleration about the z-axis— and is one of the threecomponents that completely describe the rotational acceleration of theskull. Thus, the rotational acceleration appears in the function informula (1) above as the offset and can be easily determined from theselected best fit curve. The antero-posterior and medial-lateral bendingacceleration of the skull are computed together by multiplying theestimated linear acceleration by the distance to the center of rotationof the neck for the given impact direction. This distance can be fixedfor all impact directions, selected from a lookup table, or measuredempirically. The estimate of the magnitude of the rotationalacceleration of the skull is given as the magnitude of the axial,antero-posterior and medial-lateral bending acceleration of the skull

[0068] Therefore, a further novel aspect of the system and method of thepresent invention is that computation of rotational acceleration isbased on the impact location. Such a computation is made even withoutthe assumption of orthogonality of the accelerometers relative to eachother and computation of the impact vector using the fitting algorithmdescribed above to collected data all using only single-axisaccelerometers orthogonal to the surface of a body part.

[0069] The algorithm set forth above in formula (1) has been validatedby comparison to theoretical and experimental data. The known inputswere: 1) number of accelerometers; 2) location on the transverse planeof the head of each accelerometer (measured in degrees), and, 3)magnitude (g's) and location (degrees) of the impact in the HCS. Tovalidate the algorithm, a sensitivity analysis of the independentvariables was performed. For a given set of these input variables, thecorrect (ideal) accelerations were calculated. To simulate variabilitythat would be expected in practical applications of system 30, randomnoise was added to the location of the accelerometers 14 and to theacceleration values. The algorithm used this noisy data set (repeated 10times for each parametric set of input variables) to predict themagnitude and location of the simulated hit. These values were thencompared to the input (ideal) values. Parametric analyses were performedby changing the number of accelerometers 14, the location of eachaccelerometer 14 location, the standard deviation of the noise in thelocation of the accelerometers, and the standard deviation of the noisein the peak acceleration values of each accelerometer.

[0070] Sensitivity analyses showed that computed values for peak linearhead acceleration and hit location were most sensitive to errors inaccelerometer location compared to errors in acceleration magnitude.Table 2 below summarizes the effect on both estimated accelerationparameters and on commercial factors including cost and practicalimplementation. TABLE 2 Effect on Effect on Decreasing Decreasing Errorin Error in Estimated Estimated Effect on Peak Impact Effect PracticalAcceleration Location on Implementation Compared Compared System ofSystem Parameter to Actual to Actual Cost in Helmets Increased ++ ++ + +HMAS Measurement Accuracy Increased ++++ ++++ + +++ HMAS LocationAccuracy Increased +++ +++ +++ ++++ Number of HMAS Units

[0071] A configuration with 3 accelerometers spaced equally around thecoordinate system of FIG. 3 at 120° was sufficient, as shown in FIG. 9,to achieve errors in acceleration magnitude of less than 10%. From apractical perspective, a 3 accelerometer system, with positions at 0°,120°, −120° (0° was chosen as rear of the head, negative as left sideand positive as right side from a rear view of the head as in FIG. 3),demonstrated minimum error in peak acceleration predicted with noisyacceleration data compared to the actual (ideal) input peak accelerationand impact location across all impact locations on the transverse plane.Maximum error was less than 10%. Accuracy did not begin to fall offsubstantially until the 3 accelerometers were within 30 degrees of oneanother. There was also only slight decrease in accuracy forasymmetrical accelerometer placements, such as 0°, 90°, −45°, which maybe a more practical position for the units to be placed in the helmet.For brevity, the full parametric analysis is not reported.

[0072] Increasing from three accelerometers to six accelerometersresulted in a negligible increase in the accuracy of the estimated peakacceleration and estimated impact location for a given accelerometerconfiguration.

[0073] Increasing the number of accelerometers decreased error inestimated peak acceleration and impact location error for 30 g impactsimulations (n=10) when the system variables accelerometer accelerationand accelerometer location were perturbed with random noise of 5% and 5degrees, respectively.

[0074] For any single simulation at any hit location, the error did notexceed 10% or 10 degrees. It is concluded that as long as theaccelerometer is accurate to within 5% and its location is known within5 degrees, there is no substantial benefit to increasing the number ofaccelerometers from three to six. The three accelerometer configurationis preferred from a cost and data management perspective, and meets thedesired specifications.

[0075] Experimental Testing:

[0076] Laboratory testing with a three accelerometer configurationdemonstrated that linear accelerations computed from the measuredaccelerometer accelerations were within 10% for impacts in thetransverse plane when compared to an accelerometer at the center ofgravity of the headform. Impact location was computed to be within 10°of the actual value. Estimates of rotational accelerations using linearaccelerometers were within 10% of computed values using video and directmeasurement techniques.

[0077] A standard twin-wire drop system (ASTM F1446) was utilized forlinear acceleration testing with a triaxial accelerometer mounted at thecenter of gravity of a standard ISO headform. Peak acceleration fromeach of the three accelerometers was used as input for estimating thelinear acceleration using the least squares fit algorithm describedabove.

[0078] Actual accelerometer locations were measured using a laserprotractor system. Five impacts at an impact velocity of approximately2.2 m/s were recorded at 45° intervals around the transverse plane ofthe headform. Computed peak acceleration data were compared with linearaccelerations measured by a triaxial accelerometer located at the centerof gravity of the headform.

[0079] A separate guided drop tower (not shown) with free 2D rotationwas utilized to compare measured linear and rotational accelerationsfrom both accelerometers and triaxial accelerometer at the center ofgravity of the headform with 2D rotational accelerations?? measuredusing a magnetohydrodynamic rotational velocity sensor, such as theARS-01 from Phoenix, Ariz., and computed from a 2D high speed digitalvideo system, such as Redlakes MotionScope (2000 Hz). Accelerationsmeasured by the accelerometers and by the triaxial accelerometer are acombination of linear acceleration and the normal component of therotational acceleration.

[0080] The normal component: a_(n)=rω², can then be solved for ω anddifferentiated to determine the rotational acceleration. Alternatively,the tangential component: at a_(t)=rα, can be solved directly for α, therotational acceleration. We assume that the head and neck acts as arigid body during the impact. The radius, r, was the distance from thepivot point on the experimental apparatus and the center of gravity ofthe headform. Error analysis was performed by comparing 2D rotationalaccelerations estimated from our system with the calculated rotationalaccelerations from the high-speed video and the ARS sensor. For example,for a 2.2 m/sec drop, rotational accelerations on the order of 2000rad/sec² were measured from the video, and compared with an estimated1900 rad/sec² from the linear accelerometers, representing approximately5% difference.

[0081] Thus, the algorithm in accordance with the present invention wasvalidated by demonstrating that the error in estimated peak accelerationand estimated impact location was within ±10% of actual (ideal) when thesystem variables accelerometer acceleration and accelerometer locationwere perturbed with random noise of 5% and 5 degrees, respectively. Thestandard error bars, shown in FIG. 9, illustrate variability with 10simulations.

[0082] Estimates of linear and rotational acceleration from experimentaldata collected with the system 30 were within ±10% of peak accelerationcompared to acceleration measurements taken at the center of gravity ofthe test headform. Reproducibility of the system was within ±5%.

[0083] As shown above, the algorithm for estimating linear androtational acceleration and magnitude has been validated for 2D and forimpacts along the transverse plane. In accordance with the presentinvention, the algorithm can be readily modified to 3D and tested boththeoretically and experimentally.

[0084] Therefore, the present invention provides for single axisaccelerometers to be incorporated into an helmet such that theaccelerometer is in apposition to the surface of the head and can wornby a user. Dual and tri-axis accelerometers may also be used to collectand record additional information, such as acceleration tangent to thesurface of the skull, for further analysis and study.

[0085] The system 30 of the present invention enables the relationshipbetween biomechanical measures of linear and rotational acceleration andthe clinically determined incidence of MTBI across demographic groups tobe quantified, with a particular emphasis on children and youth insports. The system 30 is capable of automatic monitoring of impactincidence and will provide a basis for testing hypotheses relatingimpact severity and history to MTBI.

[0086] It would be appreciated by those skilled in the art that variouschanges and modifications can be made to the illustrated embodimentswithout departing from the spirit of the present invention. All suchmodifications and changes are intended to be covered by the appendedclaims.

What is claimed is:
 1. A device for monitoring the acceleration of abody part having an outer surface, comprising: a plurality of sensingdevices constructed and arranged orthogonal to the outer surface of thebody part to detect acceleration; the plurality of sensing devices beingconstructed and arranged to generate a signal in response to a sensedacceleration; a processing device connected to the plurality of sensingdevices and being constructed and arranged to receive signals from theplurality of sensing devices and determine the magnitude and directionof an impact to the body part.
 2. The device of claim 1, wherein saidplurality of sensing devices are single-axis linear accelerometers. 3.The device of claim 1, wherein said plurality of sensing devices aremulti-axis linear accelerometers with at least one axis thereof beingorthogonal to the outer surface of the body part.
 4. The device of claim1, further comprising: a protective layer of material positioned aboutthe body part; a plurality of portions of cushioning material disposedbetween the body part and the protective layer of material;
 5. Thedevice of claim 5, further comprising: a carrier web being closelyfitted around the body part; the plurality of sensing devices beingattached to the carrier web and positioned orthogonal and proximal tothe outer surface of the body part.
 6. The device of claim 5, furthercomprising: a plurality of carrier clips positioned between theplurality of portions of cushioning material; the carrier clipsrespectively carrying the plurality of sensing devices and beingpositioned orthogonal and proximal to the outer surface of the bodypart.
 7. The device of claim 5, wherein the plurality of sensing devicesare embedded within the plurality of portions of cushioning material andare positioned orthogonal and proximal to the outer surface of the bodypart.
 8. The device of claim 1, wherein the plurality of sensing devicesare three devices positioned 120 degrees apart from one another aboutthe circumference of the body part.
 9. The device of claim 1, furthercomprising: a recording station connected to the plurality of sensingdevices;
 10. The device of claim 9, wherein the recording station isconnected to the plurality of sensing devices by wire.
 11. The device ofclaim 9, wherein the recording station is connected to the plurality ofsensing devices by radio transmission.
 12. The device of claim 1,wherein the body part is a head.
 13. The device of claim 1, wherein saidplurality of sensing devices are mounted in a helmet.
 14. The device ofclaim 1, wherein said plurality of sensing devices are mounted in a headband.
 15. A method for determining the magnitude and direction of impactto a body part having a geometric shape, comprising the steps of:positioning a plurality of accelerometers proximate to the outer surfaceof a body part; orienting the plurality of accelerometers to senserespective linear acceleration orthogonal to the surface of the bodypart; positioning the plurality of accelerometers in a definedarrangement about the surface of the body part; recording accelerationdata sensed by the plurality of accelerometers; providing a hit profilefunction from the geometric shape of the body part and the positioningof the plurality of accelerometers thereabout; generating a plurality ofpotential hit results from the hit profile function; comparing theplurality of potential hit results to the acceleration data sensed bythe plurality of accelerometers; best fit matching one of the potentialhit results to the acceleration data to determine a best fit hit result;and determining the magnitude of linear acceleration and the directionof an impact to the body part from the best fit hit result.
 16. Themethod of claim 15, wherein the surface of the body part is defined bythe circumference of the body part, along which the plurality ofaccelerometers is approximately a circle.
 17. The method of claim 16,wherein the hit profile function is equal to a * cos (s−b)+c where a isthe impact magnitude, s is the arc defining the accelerometer position,b is the impact direction and c is the radial acceleration due to purerotation about the superior-inferior Z-axis and known data ranges areemployed to generate potential hit results.
 18. The method of claim 15,wherein the configuration of the body part is a geometric shape.
 19. Themethod of claim 18, wherein the configuration of the profile generatingfunction corresponds to the geometric shape.
 20. The method of claim 15,wherein matching one of the potential hit profiles to the accelerationdata employs least-squares regression model to determine the best fitprofile.
 21. The method of claim 15, further comprising: estimating therotational acceleration of the body part from the magnitude of linearacceleration and the location of the impact to the body part from thebest fit hit result by multiplying the distance from the location of theimpact to an axis of rotation of the body part by the magnitude of thelinear acceleration of the body part.
 22. A method of accelerationmonitoring, comprising the steps of: attaching anacceleration-monitoring technology device, having acceleration sensors,to an individual such that the acceleration sensors remain fixedrelative to a body part of the individual during physical activity wherethe body part has an outer surface; measuring accelerations of the bodypart of the individual during physical activity along at least a first,a second and a third acceleration measurement direction, wherein thefirst acceleration measurement direction is orthogonal to the outersurface of the body part, and the second acceleration measurementdirection is orthogonal to the outer surface of the body part, and thethird acceleration measurement direction is orthogonal to the outersurface of the body part; storing the accelerations of the body part ofthe individual during the physical activity as acceleration data in amass storage device; retrieving the acceleration data of the body partof the individual during physical activity; determining a direction andmagnitude of the impact to the body part of the individual during thephysical activity and the rotational acceleration of the body part ofthe individual during the physical activity from the acceleration data.